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## Copyright (C) 2005-2021 The Octave Project Developers
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## See the file COPYRIGHT.md in the top-level directory of this
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## -*- texinfo -*-
## @deftypefn {} {[@var{ver}, @var{url}] =} get_forge_pkg (@var{name})
## Try to discover the current version of an Octave Forge package from the web,
## using a working internet connection and the urlread function.
## If two output arguments are requested, also return an address from which
## to download the file.
## @end deftypefn

function [ver, url] = get_forge_pkg (name)

  ## Verify that name is valid.
  if (! (ischar (name) && rows (name) == 1 && ndims (name) == 2))
    error ("get_forge_pkg: package NAME must be a string");
  elseif (! all (isalnum (name) | name == "-" | name == "." | name == "_"))
    error ("get_forge_pkg: invalid package NAME: %s", name);
  endif

  name = tolower (name);

  ## Try to download package's index page.
  [html, succ] = urlread (sprintf ("https://packages.octave.org/%s/index.html",
                                   name));
  if (succ)
    ## Remove blanks for simpler matching.
    html(isspace(html)) = [];
    ## Good.  Let's grep for the version.
    pat = "<tdclass=""package_table"">PackageVersion:</td><td>([\\d.]*)</td>";
    t = regexp (html, pat, "tokens");
    if (isempty (t) || isempty (t{1}))
      error ("get_forge_pkg: could not read version number from package's page");
    else
      ver = t{1}{1};
      if (nargout > 1)
        ## Build download string.
        pkg_file = sprintf ("%s-%s.tar.gz", name, ver);
        url = ["https://packages.octave.org/download/" pkg_file];
        ## Verify that the package string exists on the page.
        if (isempty (strfind (html, pkg_file)))
          warning ("get_forge_pkg: download URL not verified");
        endif
      endif
    endif
  else
    ## Try get the list of all packages.
    [html, succ] = urlread ("https://packages.octave.org/list_packages.php");
    if (! succ)
      error ("get_forge_pkg: could not read URL, please verify internet connection");
    endif
    t = strsplit (html);
    if (any (strcmp (t, name)))
      error ("get_forge_pkg: package NAME exists, but index page not available");
    endif
    ## Try a simplistic method to determine similar names.
    function d = fdist (x)
      len1 = length (name);
      len2 = length (x);
      if (len1 <= len2)
        d = sum (abs (name(1:len1) - x(1:len1))) + sum (x(len1+1:end));
      else
        d = sum (abs (name(1:len2) - x(1:len2))) + sum (name(len2+1:end));
      endif
    endfunction
    dist = cellfun ("fdist", t);
    [~, i] = min (dist);
    error ("get_forge_pkg: package not found: ""%s"".  Maybe you meant ""%s?""",
           name, t{i});
  endif

endfunction